The following abbreviations and acronyms are herewith defined, at least some of which are referred to within the following description.
Third Generation Partnership Project (“3GPP”), Positive-Acknowledgment (“ACK”), Acknowledgment Mode (“AM”), Access and Mobility Management Function (“AMF”), Control Channel Element (“CCE”), Control Plane Function (“CPF”), Channel State Information (“CSI”), Common Search Space (“CSS”), Data Radio Bearer (“DRB”), Downlink (“DL”), Evolved Node B (“eNB”), European Telecommunications Standards Institute (“ETSI”), Frequency Division Duplex (“FDD”), Frequency Division Multiple Access (“FDMA”), Hybrid Automatic Repeat Request (“HARQ”), Information Element (“IE”), Long Term Evolution (“LTE”), LTA Advanced (“LTE-A”), Medium Access Control (“MAC”), Modulation Coding Scheme (“MCS”), Multiple Input Multiple Output (“MIMO”), Multipath TCP (“MPTCP”), Narrowband (“NB”), Negative-Acknowledgment (“NACK”) or (“NAK”), Network Function (“NF”), Next Generation Node B (“gNB”), Orthogonal Frequency Division Multiplexing (“OFDM”), Physical Broadcast Channel (“PBCH”), Packet Data Convergence Protocol (“PDCP”), Packet Data Unit (“PDU”), Physical Downlink Control Channel (“PDCCH”), Physical Downlink Shared Channel (“PDSCH”), Physical Hybrid ARQ Indicator Channel (“PHICH”), Physical Random Access Channel (“PRACH”), Physical Resource Block (“PRB”), Physical Uplink Control Channel (“PUCCH”), Physical Uplink Shared Channel (“PUSCH”), Quality of Service (“QoS”), Quadrature Phase Shift Keying (“QPSK”), Radio Link Control (“RLC”), Radio Resource Control (“RRC”), Random Access Procedure (“RACH”), Random Access Response (“RAR”), Radio Bearer (“RB”), Receive (“RX”), Service Data Unit (“SDU”), Switching/Splitting Function (“SSF”), Scheduling Request (“SR”), Session Management Function (“SMF”), Shared Channel (“SCH”), Signal-to-Interference-Plus-Noise Ratio (“SINR”), System Information Block (“SIB”), Transport Block (“TB”), Transport Block Size (“TBS”), Transmission Control Protocol (“TCP”), Time-Division Duplex (“TDD”), Time Division Multiplex (“TDM”), Transmission and Reception Point (“TRP”), Transmission Time Interval (“TTI”), Transmit (“TX”), Uplink Control Information (“UCI”), User Datagram Protocol (“UDP”), User Entity/Equipment (Mobile Terminal) (“UE”), Uplink (“UL”), User Plane Function (“UPF”), Universal Mobile Telecommunications System (“UMTS”), and Worldwide Interoperability for Microwave Access (“WiMAX”). As used herein, “HARQ-ACK” may represent collectively the Positive Acknowledge (“ACK”) and the Negative Acknowledge (“NAK”). ACK means that a TB is correctly received while NAK means a TB is erroneously received.
In 5G networks, a source gNB (or other 5G base station) may handover a UE using a conditional handover to increase the reliability of the handover command and thus provide improved handover performance. After sending the conditional handover command, the source gNB forwards data to the target gNB and also attempts to deliver this data to the UE. However, the UE may spend some considerable amount of time in the source cell after receiving the conditional handover command, the UE being scheduled until it executes the handover (e.g., when the handover condition is fulfilled), leading to a large amount of data being forwarded to the target gNB. The target gNB is unaware which data was successfully transmitted in the source cell. Hence, the target gNB may unnecessarily retransmit a significant amount of data for the conditional handover case.